Wireless data transmission in CT-scanners

ABSTRACT

A CT-scanner having a gantry comprising a stator and a rotor, wherein an X-ray source and array of X-ray detectors are mounted to the rotor for determining absorption of X-rays along paths through the body of a patient imaged by the CT-scanner, the CT imager comprising: a processor that processes data comprised in signals generated by the X-ray detectors responsive to intensity of X-rays from the X-ray source incident on the detectors to generate an image of the patient; at least one spread spectrum transmitter that receives data comprised in the signals generated by the X-ray detectors and transmits signals encoded with the data in accordance with a spread spectrum coding; and at least one spread spectrum receiver that receives the encoded signals transmitted by the at least one spread spectrum transmitter and forwards the encoded data to the processor.

RELATED APPLICATIONS

This application is a U.S. national filing of PCT Application No.PCT/US01/49152, filed on Dec. 19, 2001.

FIELD OF THE INVENTION

The present invention relates to computerized tomography (CT) X-rayimaging, and in particular to methods to methods and apparatus fortransmitting data generated by X-ray detectors in a CT-scanner to aprocessor that generates and displays images responsive to the data.

BACKGROUND OF THE INVENTION

In CT X-ray imaging of a patient, X-rays are used to image internalstructure and features of a region of the person's body. The imaging isperformed by a CT-imaging system, hereinafter referred to as a“CT-scanner” that images internal structure and features of a pluralityof contiguous relatively thin planar slices of the body region usingX-rays.

The CT-scanner generally comprises an X-ray source that provides aplanar, fan-shaped X-ray beam and an array of closely spaced X-raydetectors that are coplanar with the fan beam and face the X-ray source.The X-ray source and array of detectors are mounted in a gantry so thata person being imaged with the CT-scanner, generally lying on anappropriate support couch, can be positioned within the gantry betweenthe X-ray source and the array of detectors. The gantry and couch aremoveable relative to each other so that the X-ray source and detectorarray can be positioned axially at desired locations along the patient'sbody.

The gantry comprises a stationary structure referred to as a stator anda rotary element, referred to as a rotor, which is mounted to the statorso that the rotor is rotatable about the axial direction. In thirdgeneration CT-scanners the X-ray source and detectors are mounted to therotor. Angular position of the rotor about the axial direction iscontrollable so that the X-ray source can be positioned at desiredangles, referred to as “view angles”, around the patient's body.

To image a slice in a region of a patient's body, the X-ray source ispositioned at the axial position of the slice and the X-ray source isrotated around the slice to illuminate the slice with X-rays from aplurality of different view angles. At each view angle, detectors in thearray of detectors measure intensity of X-rays from the source that passthrough the slice. The intensity of X-rays measured by a particulardetector in the array of detectors is a function of an amount by whichX-rays are attenuated by material in the slice along a path length fromthe X-ray source, through the particular slice, to the detector. Themeasurement provides information on composition and density of tissue inthe slice along the path-length.

For example, let incident X-ray intensity sensed by an “n-th” detectorin the array of detectors when the X-ray source is located at a viewangle θ is represented by I(n,θ), then I(n,θ)=I_(O)exp(−∫μ(l)dl). In theexpression for I(n,θ), I_(O) is intensity of X-rays with which the X-raysource illuminates the slice, integration over l represents integrationover a path through material in the slice along a direction from theX-ray source to the n-th detector and μ(l) is an absorption coefficientfor X-rays per unit path-length in the material at position l along thepath. (Dependence of the integral on n and θ is not shown explicitly andis determined through dependence of the length and direction of thepath-length l on n and θ.)

From I_(O) and the sensed I(n,θ), an amount by which X-rays areattenuated along path-length l and a value for the integral ∫μ(l)dl,hereinafter referred to as an “line integral”, can be determined. Theattenuation measurement provided by the n-th detector at the view angleθ therefore provides a value for the line integral of the absorptioncoefficient along a particular path length through the slice which isdetermined by θ and the known position of the n-th detector relative tothe X-ray source.

The set of attenuation measurements for a slice provided by all thedetectors in the detector array at a particular view angle θ is referredto as a view. The set of attenuation measurements from all the views ofthe slice is referred to as a “projection” of the slice. Values for theline integral provided by data from the projection of the slice areprocessed using algorithms known in the art to provide a map of theabsorption coefficient μ as a function of position in the slice. Maps ofthe absorption coefficient for the plurality of contiguous slices in theregion of the patient's body are used to display and identify internalorgans and features of the region.

In some CT-scanners, to image a region of a patient, a sequential scanof the patient is performed in which the region is scanned by moving thepatient stepwise in the z direction to “step” the region through thegantry that houses the X-ray source and detector array. Following eachstep, the X-ray source is rotated through 360 degrees or (180+Δ)degrees, where Δ is an angular width of the fan beam provided by theX-ray source, to acquire a projection of a slice of the region. In someCT-imagers a “spiral scan” of a patient is performed in which the regionof the patient is steadily advanced through the gantry while the X-raysource simultaneously rotates around the patient and projections ofslices in the region are acquired “on the fly”. In some CT-scanners,referred to as multislice CT-scanners, a plurality of slices of a regionof a patient are simultaneously imaged. Often as many as four slices ofa region of a patient are simultaneously imaged by a multisliceCT-scanner.

In third generation CT-scanners the X-ray source and the detectors aremounted on the imager's rotor. Data generated by the detectorsresponsive to intensity of X-rays incident on the detectors has to betransferred from the rotor to a location of a processor that generatesimages from the data and displays the generated images.

Many different methods and systems are available for transmitting datagenerated by detectors on the rotor of a CT-scanner to a desiredlocation for processing and display. However, the immediate environmentof the rotor is generally electromagnetically very noisy. As a result,free space transmission of the data using electromagnetic waves has notbeen considered practical. Usually, data generated by the detectors istransferred from the rotor over very short distances to the stator viacontact connections or non-contact “proximity” connections between therotor and stator. From the stator the data is transmitted via wire oroptical fiber to a desired location where the data is processed and/ordisplayed.

In some third generation CT-scanners electromechanical, contactslip-rings provide contact connections between the imager's rotor andstator for transmitting data from the rotor to the stator. However,present day CT-scanners generate data at data rates between 20-800Mbits/s and data rates are increasing as CT-scanners become faster andmultislice CT-scanners acquire projections of an increasing plurality ofslices simultaneously. Contact slip-rings generally cannot supportreliable data transfer at data transfer rates that match rates at whichmodern third generation CT-scanner generate data.

Usually therefore, in modem CT-scanners data is transmitted between therotor and stator via non-contact proximity links, which links may, forexample, be optical or electromagnetic. Various types of suchnon-contact links are commercially available, for example, fromSchliefring (Germany), Litton Poly-Scientific (USA) and ElectroTech(USA). However, currently available non-contact links for CT-scannersare generally expensive and they usually complicate mechanicalconstruction of the imagers. Furthermore, present non-contact linksgenerally cannot support data transfer rates about equal to or greaterthan 1 Gbit/sec.

U.S. Pat. No. 5,577,026 describes a non-contact data link fortransferring data between the rotor and stator of a CT-scanner in whichthe data is transferred via antenna assemblies on the rotor and stator.In an embodiment of the data link the antenna assemblies arecapacitively coupled and data is transferred between the antenna usingRF signals. The inventors note that IR, UV or optical frequencies mayalso be used to transfer data. The inventors describe coding datatransmitted over the link using an Ethernet protocol and achievingreliable data transfer rates of approximately 10 megabits per second(Mbits/s).

U.S. Pat. No. 5,530,425 describes a system for transmitting data from aCT-scanner rotor to the imager stator using a transmission line mountedon the rotor and a non-contact proximity RF coupler mounted on thestator which is coupled to the transmission line. The inventor notesthat the system supports data transmission rates at 150 Mbits/s.

U.S. Pat. No. 5,469,488 describes an optical system for transmittingdata between the rotor and stator of a CT-scanner. A plurality of lightemitting elements in the system is located on the rotor or stator andtransmits optical signals to a light receiving element mountedrespectively on the stator or the rotor to transfer data between thestator and rotor.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates toproviding a method and apparatus for transmitting data generated byX-ray detectors mounted in a rotor of a CT-scanner gantry to a receiverat a desired location, using free space electromagnetic waves.

An aspect of some embodiments of the present invention relates toproviding a method and apparatus for transmitting data generated by theX-ray detectors to a receiver that is located at a position removed formthe rotor.

An aspect of some embodiments of the present invention relates toproviding a method and apparatus for transmitting data from thedetectors that supports reliable data transmission at transmission ratesequal to or in excess of 1 Gbit/s.

The inventors have realized that data can be reliably transmitted overfree space at high data rates from detectors in a rotor of a CT-scannerto a desired location using spread spectrum coding of electromagneticwaves. Spread spectrum transmission is particularly robust and can beused to reliably and accurately transmit data between locations in anelectronically noisy environment via free space electromagnetic waves.

In particular, a spread spectrum transmission technique referred to as“time hopping impulse modulation”, hereinafter “THIM”, can be used tosupport reliable, simultaneous data transmission from a large number ofdata sources located in a same localized noisy environment. In THIMtransmission a signal is transmitted as a pulse train of very shortpulses, referred to as impulses or monopulses. Each monopulse and a nextsubsequent monopulse in the pulse train are separated by a time period,referred to as pulse repetition intervals (PRI). The PRIs are generallymuch longer than a duration of a monopulse and may range from hundredsto thousands of times longer than a duration of a monopulse. The PRIbetween any two consecutive monopulses is regularly changed inaccordance with a predetermined periodic “time hopping code”. Data isencoded into the pulse train by making changes in the PRIs, which areadditional to those changes made responsive to the time hopping code,that are determined responsive to the data to be encoded. Many THIMtransmitters operating in a same neighborhood can usually simultaneouslytransmit data to a same receiver without data transmitted by one of thetransmitters interfering with data transmitted by another of thetransmitters. Interference is generally prevented or substantiallyreduced by operating each of the different transmitters using adifferent time hopping code.

THIM is described in a series of patents to Fullerton beginning withU.S. Pat. No. 4,641,317, which issued on Feb. 3, 1987, and which wasfollowed by U.S. Pat. Nos. 4,813,057, 4,979,186, and 5,363,108. U.S.Pat. No. 6,031,862, also to Fullerton, notes that theoretical analysissuggests that an RF THIM system can provide thousands of voice channelsper cell in a cellular phone system. The disclosures of all the abovenoted patents to Fullerton are incorporated herein by reference.

In accordance with an embodiment of the present invention, a CT-scanneris provided comprising a data transmission system having at least oneTHIM transmitter for transmitting data from X-ray detectors mounted onthe rotor of the imager to a desired location. In some embodiments ofthe present invention, the at least one THIM transmitter transmits datafrom the detectors to a THIM receiver on the gantry stator. Unlike inprior art systems for transmitting data from the rotor to the stator,THIM transmission of data from the rotor to the stator, in accordancewith an embodiment of the present invention, does not require that theTHIM transmitter and receiver be in physical contact or in closeproximity. As a result, use of THIM transmission simplifies constructionof the gantry.

In some embodiments of the present invention, the at least one THIMtransmitter transmits data from the detectors in the rotor to a receiverlocated at a distance from the gantry rather than to a receiver on thestator. For example, a receiver may be located in a different part of asame room in which the CT-gantry is located. Since THIM signals canrelatively easily be detected after being transmitted through most wallsof a building, a receiver may, be in a room different from a room inwhich the CT-gantry is located. For example, in some embodiments of thepresent invention a receiver is located at a venue at which the data isprocessed and/or displayed, which venue may be located in a roomdifferent from the room in which the CT-gantry is located.

As noted above, since many THIM transmitters can be operatedsimultaneously to transmit data, a data transmission system, inaccordance with an embodiment of the present invention, can beconfigured to support a large data transmission rate by providing thesystem with a sufficient number of THIM transmitters. For example, aTHIM transmitter that supports data transmission rates up to about 40Mbit/sec is currently available from “Time Domain” of Alabama USA in achipset called “PulsOn. To provide a data transmission system for aCT-system that supports a transmission rate of about 1.2 Mbit/sec thesystem can be configured to comprise 30 PulsOn chipsets operating inparallel.

In some embodiments of the present invention, data generated by thedetectors is preprocessed at the rotor by a suitable processor and thepreprocessed data is then transmitted to a receiver by the at least oneTHIM transmitter. Preprocessing might include for example, in accordancewith an embodiment of the present invention, packing the data into datapackets having identifying headers and comprising various errorcorrection codes of types known in the art. In some embodiments of thepresent invention, the headers are used by the receiver to identify datapackets that are not received or are corrupted. For missing and/orcorrupted data packets the receiver initiates a redundancy protocol inwhich a missing and/or corrupted packet is retransmitted by the at leastone THIM transmitter.

There is therefore provided in accordance with an embodiment of thepresent invention, A CT-scanner having a gantry comprising a stator anda rotor, wherein an X-ray source and array of X-ray detectors aremounted to the rotor for determining absorption of X-rays along pathsthrough the body of a patient imaged by the CT-scanner, the CT imagercomprising: a processor that processes data comprised in signalsgenerated by the X-ray detectors responsive to intensity of X-rays fromthe X-ray source incident on the detectors to generate an image of thepatient; at least one spread spectrum transmitter that receives datacomprised in the signals generated by the X-ray detectors and transmitssignals encoded with the data in accordance with a spread spectrumcoding; and at least one spread spectrum receiver that receives theencoded signals transmitted by the at least one spread spectrumtransmitter and forwards the encoded data to the processor.

Optionally, the at least one transmitter comprises at least one timehopping impulse modulation (THIM) transmitter that transmits signalsencoded with the data in accordance with a THIM code and the at leastone receiver comprises at least one THIM receiver that receives theencoded signals transmitted by the at least one THIM transmitter.Additionally or alternatively, the signals encoded with the data arefree space electromagnetic waves encoded with the data.

There is further provided in accordance with an embodiment of thepresent invention, a CT-scanner having a gantry comprising a stator anda rotor, wherein an X-ray source and array of X-ray detectors aremounted to the rotor for determining absorption of X-rays along pathsthrough the body of a patient imaged by the CT-scanner, the CT imagercomprising: a processor that processes data comprised in signalsgenerated by the X-ray detectors responsive to intensity of X-rays fromthe X-ray source incident on the detectors to generate an image of thepatient; at least one transmitter that receives data comprised in thesignals generated by the X-ray detectors and transmits free spaceelectromagnetic waves encoded with the data; at least one receiver thatreceives the encoded free space electromagnetic waves transmitted by theat least one transmitter and forwards the encoded data to the processor.

Optionally, the at least one transmitter comprises at least one spreadspectrum transmitter that encodes the data in the free spaceelectromagnetic waves in accordance with a spread spectrum code and theat least one receiver comprises at least one spread spectrum receiver.

Optionally, the at least one transmitter comprises at least one THIMtransmitter that encodes the data in the free space electromagneticwaves in accordance with a THIM code and the at least one receivercomprises at least one THIM receiver.

In some embodiments of the present invention, the transmitter andreceiver are located in a same room.

In some embodiments of the present invention, the transmitter is locatedon the gantry and the receiver is at a distance from the gantry.Optionally, the transmitter and receiver are located in different rooms.

In some embodiments of the present invention, the transmitter is locatedon the stator.

In some embodiments of the present invention, the transmitter is locatedon the rotor.

In some embodiments of the present invention, the transmitter is locatedon the rotor and the at least one receiver is located on the stator.

In some embodiments of the present invention, the at least one receiverand the processor are near each other in a same location.

In some embodiments of the present invention, the receiver and theprocessor are in different rooms.

In some embodiments of the present invention, the at least one receiveris connected to the processor by wire over which the receiver forwardsthe data to the processor.

In some embodiments of the present invention, the at least one receiveris connected to the processor by optical fiber over which the receiverforwards the data to the processor.

In some embodiments of the present invention, the at least onetransmitter comprises a plurality of transmitters. Optionally, thetransmitters transmit simultaneously.

Alternatively, or additionally, the at least one receiver comprises aplurality of receivers. Optionally, at least two of the plurality ofreceivers receives transmissions from different transmitters.

In some embodiments of the present invention, the CT-scanner comprisesat least one data acquisition system (DAS) mounted on the rotorconnected to the X-ray detectors that receives the signals generated bythe X-ray detectors and generates digital data therefrom, portions ofwhich digital data the at least one DAS routes to each of the at leastone transmitter. Optionally, the at least one DAS comprises a pluralityof DASs each of which acquires signals from different detectors.

There is further provided in accordance with an embodiment of thepresent invention, a method of transmitting to a desired location datacomprised in signals generated by X-ray detectors mounted on a rotor ofa gantry comprised in a CT-scanner, the method comprising: generatingfree space electromagnetic waves encoded with the data; sensing theelectromagnetic waves at the desired location; and decoding the sensedelectromagnetic wave to recover the data.

Optionally, the data is encoded in accordance with a spread spectrumcode. Optionally, the data is encoded in accordance with a time hoppingimpulse modulation (THIM) code. There is further provided in accordancewith an embodiment of the present invention, a method of transmitting toa desired location data comprised in signals generated by X-raydetectors mounted on a rotor of a gantry comprised in a CT-scanner, themethod comprising: generating signals encoded with the data inaccordance with a spread spectrum code; sensing the signals at thedesired location; and decoding the sensed signals to recover the data.Optionally, the code is a THIM code. Additionally or alternatively thesignals encoded with the data are free space electromagnetic wavesencoded with the data.

BRIEF DESCRIPTION OF FIGURE

Non-limiting examples of embodiments of the present invention aredescribed below with reference to:

FIG. 1, which schematically shows a CT-scanner having a datatransmission system that comprises at least one THIM transmitter, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 schematically shows a third generation CT-scanner 20 comprising aTHIM data transmission system, in accordance with an embodiment of thepresent invention. In FIG. 1, by way of example CT-scanner 20 is shownimaging a region of the chest of a patient 22. Dimensions of componentsand features shown in the FIGURE are chosen for convenience and clarityof presentation and are not necessarily shown to scale.

CT-scanner 20 comprises an X-ray source 24 controllable to provide afan-beam schematically indicated by dashed lines 26 and an array 30 ofX-ray detectors 32 mounted opposite the X-ray source for sensing X-raysin the fan-beam. CT-scanner 20 is assumed, by way of example to be amultislice imager that simultaneously images a plurality of four slicesof a region of the body of a patient (patient 22 in FIG. 1) being imagedwith the CT-scanner. Detectors 32 in array 30 are therefore configuredin a plurality of four contiguous curved rows 33 of the detectors.CT-scanner 20 comprises a gantry 34 having a stator 35 to which a rotor36 is mounted so that the rotor can be controlled to rotate about anaxis 37. X-ray source 24 and detector array 30 are fixedly mounted torotor 36 so that when rotor 36 rotates about axis 37 the X-ray sourceand detector array also rotate about axis 37.

Patient 22 is supported on a couch 38 during imaging of the patient withCT-system 20. Couch 38 is mounted on a suitable pedestal (not shown) sothat couch 38 is controllable to be translated axially along axis 37.Detectors 32 in detector array 30 and features of CT-scanner that areshadowed by patient 22 and couch 38 and would not normally be seen inthe perspective of FIG. 1 are shown for clarity of presentation withghost lines.

For convenience, a coordinate system shown in FIG. 1 having a horizontalx-axis, vertical y-axis and z-axis coincident with axis 37, is used tolocate components and features of CT-system 20 and patient 22. Thecoordinate system is assumed to be fixed with respect to gantry 34. Viewangle of X-ray source 24 is measured with respect to the y-axis of thecoordinate system. Slices of the body of patent 22 are located by theposition of the slice along the z-axis.

To image the chest region of patient 22 couch 38 is controlled totranslate along the z-axis and move the chest region through the spacebetween X-ray source 24 and detector array 30 to expose the chest regionto X-rays and acquire views of slices of the chest region at desiredview angles. At each desired view angle detectors 32 in a row 33 ofdetectors generate signals responsive to intensity of X-rays to whichthey are exposed that provide a view of a single slice of patient 22.The four rows 33 of detectors 32 generate signals that simultaneouslyprovide views of four different slices of patient 22. In FIG. 1CT-scanner is shown, by way of example, acquiring views of four slices40 at a view angle of about 90°.

A data acquisition system (DAS) 50 and, in accordance with an embodimentof the present invention, at least one THIM transmitter 52 are mountedon rotor 36. The signals generated by detectors 32 are transferred bywire (not shown) to a data acquisition system DAS 50 mounted on rotor 36that processes the signals to generate digital data therefrom. DAS 50routes, responsive to an appropriate routing algorithm, portions of thedigital data that it generates to each of the at least one THIMtransmitter 52. Each of the at least one THIM transmitter 52 transmitsthe data that it receives as “THIM” data signals to an at least one THIMreceiver 58 located at a desired venue. THIM signals transmitted by eachTHIM transmitter 52 are schematically shown as a train 54 of monopulses56 emitted by the transmitter.

It is noted that whereas in FIG. 1 a single DAS 50 is shown, in someembodiments of the present invention a plurality of DASs is mounted onrotor 36 and that different configurations of the plurality of DASs andthe at least one THIM transmitter are possible and can be advantageous.For example, a different DAS of the plurality of DASs may be associatedwith each row 33 of detectors 32 and each DAS may route digital datathat it generates to a different THIM transmitter or transmitters.

By way of example, in FIG. 1 the at least one THIM receiver is a singleTHIM receiver 58 comprised in a processing station 60 located in a room,which is different from a room in which CT-scanner is located. A “wall”62 between CT-scanner 20 and processing station 60 schematicallyindicates that the CT-scanner and processing station may be located indifferent rooms. Processing station 60 comprises a processor 63 and avisual display console 64 for generating and displaying images ofregions of patient 22 from the data it receives from the at least oneTHIM transmitter 52.

The number of THIM transmitters comprised in CT-scanner 20 is determinedto provide sufficient transmission channel capacity to support a datarate at which detectors 32 in detector array 30 generate data. Forexample, assume that CT-scanner 20 is operated to take views of patient22 at 2320 views angles per second and that each row 33 of detectors 32comprises 672 detectors 32. Assume further that DAS 50 converts eachsignal generated by one of detectors 32 to a 16 bit word. The four rows33 of detectors 32 comprised in CT-scanner 20 therefore generate data ata rate of about 100 Mbit/sec. Assume that each THIM transmitter 52supports data transmission rates that are similar to data transmissionrates supported by the THIM transmitter provided by the Time Domain chipset PulsOn. Each PulsOn chip set provides a THIM transmitter thatsupports data transmission rates up to 40 Mbits/sec. At least three THIMtransmitters 52, in accordance with an embodiment of the presentinvention, as shown in FIG. 1, are therefore required to transmit thedata generated by CT-scanner 20.

It is noted that a data transmission system for a CT-scanner, inaccordance with an embodiment of the present invention, that comprisesTHIM transmitters is not limited to having a relatively small number ofTHIM transmitters such as the three THIM transmitters 52 shown in FIG.1. For example, assume a CT-scanner similar to CT imager 20 thatacquires views for sixteen slices simultaneously instead of for fourslices and comprises therefore sixteen rows 33 of detectors 32, eachhaving 672 detectors, instead of four rows of the detectors. Assume thatthe CT-scanner acquires views for 4640 view angles per second and thateach signal from a detector 32 in the CT-scanner is converted into asixteen bit word. The CT-scanner would generate data at a rate of about800 Mbits/sec. A data transmission system, in accordance with anembodiment of the present invention, for such a CT-scanner would have atleast twenty forty-Mbit/sec THIM transmitters 52 of the PulsOn type.

To operate each of THIM transmitters 52 simultaneously and substantiallyprevent transmission from one THIM transmitter 52 interfering withtransmission from another THIM transmitter 52, in some embodiments ofthe present invention, each THIM transmitter 52 is operated with adifferent time hopping code. FIG. 1 schematically shows each of THIMtransmitters 52 transmitting data to receiver 58 using a differenthopping code. The different hopping codes are indicated by a different“temporal” spacings, which schematically represent different PRIs, (i.e.pulse repetition intervals) between monopulses 56 in the different pulsetrains 54 emitted by the THIM transmitters 52.

In some embodiments of the present invention, each THIM transmitter 52operates with a same time hopping code. To separate transmission fromdifferent THIM transmitters 52, the transmissions from the differenttransmitters are temporally offset from each other using a methoddescribed in U.S. Pat. No. 5,537,397, the disclosure of which isincorporated herein by reference.

Optionally, processing station 60 optionally comprises a transmitter 70for transmitting control and data signals to DAS 50 and varioussubsystems (not shown) that may be mounted on rotor 36. For receivingsignals transmitted by processing station 60, a receiver 72, which isconnected to DAS 50 and the various subsystems of rotor 36, is mountedon the rotor. In some embodiments of the present invention, for whichwireless communication between processing center 60 and rotor 36 isdesired, transmission from processing station 60 to the rotor isprovided by a THIM channel and transmitter 70 is a THIM transmitter andreceiver 72 is a THIM receiver. In general, however, data traffic fromprocessing station 60 to DAS 50 is substantially less than data trafficfrom the DAS to the processing station. As a result, control and datasignal transmission from processing station 60 to rotor 36 can generallybe supported, if desired, by a relatively simple wire channel betweenthe processing station and stator 35 and a slip-ring link between thestator and rotor 36.

In accordance with some embodiments of the present invention DAS 50codes the digital data it generates in accordance with a coding schemeand error correction algorithm known in the art. For example, in someembodiments of the present invention, DAS 50 packs the data into datapackets comprising an identifying header similar to the way in whichdata is packed into data packets for transmission over a packet switchednetwork. Optionally, each data packet is coded with error correctiondata usable to correct errors that may occur in data comprised in thedata packet. DAS 50 routes the data packets so that all of each datapacket is transmitted by single THIM transmitter 52.

Processor 63 uses data in the headers of the packets it receives todetermine if it receives all the packets from DAS 50 that it shouldreceive. If processor 63 determines that a frame is missing, theprocessor transmits a message to DAS 50 instructing the DAS toretransmit the missing packet. Similarly, if processor 63 determinesthat data in a packet received by processing station 60 is so badlycorrupted that the data cannot be reconstituted using the errorcorrection data included in the data packet, the processor instructs DAS50 to resend the corrupted packet.

It is noted that error coding and packeting data generated by DAS 50adds a “data management” overhead to the transmission of data from DAS50 to processing station 60. Additional channel capacity that may berequired to support the overhead can readily be provided by increasingthe number of THIM transmitters used for transmitting data from DAS 50to processing station 60. For example, the inventors have determinedthat for the sixteen slice CT-scanner described above, which generatesdata at a rate of 800 Mbits/sec, a data management overhead of about 300Mbits/sec may be required to support packeting, error correction codingand retransmission of missing or corrupted packets. The total datatransmission rate required by the CT-scanner becomes 1.1 Gbits/sec,which transmission data rate can be provided by adding eight THIMtransmitters 52 to the twenty THIM transmitters required to transmit the800 Mbits/sec of data without the management overhead.

Methods of configuring and transmitting the data in the data streamgenerated by DAS 50 for transmission by THIM transmitters other than themanner described in the preceding paragraphs will occur to person's ofthe art. For example, in some embodiments of the present invention, DAS50 generates a plurality of simultaneous digital data streams fromsignals from X-ray detectors 32 and routes each of the data streams to adifferent one of the THIM transmitters. In addition it is noted thatconfigurations of DASs, THIM transmitters and THIM receivers differentfrom the configuration shown in FIG. 1 are possible and such differentconfigurations will occur to a person of the art and can beadvantageous. For example, the at least one THIM receiver 58 shown inFIG. 1 may comprise a plurality of THIM receivers, one for each THIMtransmitter 52 or THIM receiver 58 may be located on wall 62 and coupledby wire or an ordinary radio link to processing station 60.

It should also be noted that whereas THIM transmitters 52 in FIG. 1 areshown mounted on the rotor 36, a THIM transmitter or transmitters can,in accordance with an embodiment of the present invention,advantageously be mounted on stator 35 or in the vicinity of gantry 34.For example, THIM transmitters, which are not used to transmit data fromthe rotor of a CT-scanner to the imager's stator may be used to providewireless data channels from the electromagnetically noisy environment ofthe CT-scanner's gantry to a desired venue located at distance from thegantry. Data from the rotor to the stator may be transmitted byconventional means and from the stator to the THIM transmitter by wire.The THIM transmitter is then used to transmit the data by wirelesstransmission to, for example, a different room.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of members, components, elements or parts of thesubject or subjects of the verb.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. Variations of embodiments of the present invention that aredescribed and embodiments of the present invention comprising differentcombinations of features noted in the described embodiments will occurto persons of the art. The scope of the invention is limited only by thefollowing claims.

1. A CT-scanner having a gantry comprising a stator and a rotor, whereinan X-ray source and array of X-ray detectors are mounted to the rotorfor determining absorption of X-rays along paths through the body of apatient imaged by the CT-scanner, the CT scanner comprising: a processorthat processes data comprised in signals generated by the X-raydetectors responsive to intensity of X-rays from the X-ray sourceincident on the detectors to generate an image of the patient; at leastone spread spectrum transmitter that receives data comprised in thesignals generated by the X-ray detectors and transmits signals encodedwith the data in accordance with a spread spectrum coding; and at leastone spread spectrum receiver that receives the encoded signalstransmitted by the at least one spread spectrum transmitter and forwardsthe encoded data to the processor.
 2. A CT-scanner according to claim 1wherein the at least one transmitter comprises at least one time hoppingimpulse modulation (THIM) transmitter that transmits signals encodedwith the data in accordance with a THIM code and the at least onereceiver comprises at least one THIM receiver that receives the encodedsignals transmitted by the at least one THIM transmitter.
 3. ACT-scanner according to claim 1 wherein the signals encoded with thedata are free space electromagnetic waves encoded with the data.
 4. ACT-scanner having a gantry comprising a stator and a rotor, wherein anX-ray source and array of X-ray detectors are mounted to the rotor fordetermining absorption of X-rays along paths through the body of apatient imaged by the CT-scanner, the CT scanner comprising: a processorthat processes data comprised in signals generated by the X-raydetectors responsive to intensity of X-rays from the X-ray sourceincident on the detectors to generate an image of the patient; at leastone transmitter that receives data comprised in the signals generated bythe X-ray detectors and transmits free space electromagnetic wavesencoded with the data; at least one receiver that receives the encodedfree space electromagnetic waves transmitted by the at least onetransmitter and forwards the encoded data to the processor.
 5. ACT-scanner according to claim 4 wherein the at least one transmittercomprises at least one spread spectrum transmitter that encodes the datain the free space electromagnetic waves in accordance with a spreadspectrum code and the at least one receiver comprises at least onespread spectrum receiver.
 6. A CT-scanner according to claim 5 whereinthe at least one transmitter comprises at least one THIM transmitterthat encodes the data in the free space electromagnetic waves inaccordance with a THIM code and the at least one receiver comprises atleast one THIM receiver.
 7. A CT-scanner according to claim 1 or claim 4wherein the transmitter and receiver are located in a same room.
 8. ACT-scanner according to claim 1 or claim 4 wherein the transmitter islocated on the gantry and the receiver is at a distance from the gantry.9. A CT-scanner according to claim 8 wherein the transmitter andreceiver are located in different rooms.
 10. A CT-scanner according toclaim 7 wherein the transmitter is located on the stator.
 11. ACT-scanner according to claim 7 wherein the transmitter is located onthe rotor.
 12. A CT-scanner according to claim 1 or claim 4 wherein thetransmitter is located on the rotor and the at least one receiver islocated on the stator.
 13. A CT-scanner according to claim 1 or claim 4wherein the at least one receiver and the processor are near each otherin a same location.
 14. A CT-scanner according to claim 1 or claim 4wherein the receiver and the processor are in different rooms.
 15. ACT-scanner according to claim 1 or claim 4 wherein the at least onereceiver is connected to the processor by wire over which the receiverforwards the data to the processor.
 16. A CT-scanner according to claim1 or claim 4 wherein the at least one receiver is connected to theprocessor by optical fiber over which the receiver forwards the data tothe processor.
 17. A CT-scanner according to claim 1 or claim 4 whereinthe at least one transmitter comprises a plurality of transmitters. 18.A CT-scanner according to claim 17 wherein the transmitters transmitsimultaneously.
 19. A CT-scanner according to claim 17 wherein the atleast one receiver comprises a plurality of receivers.
 20. A CT-scanneraccording to claim 19 wherein at least two of the plurality of receiversreceives transmissions from different transmitters.
 21. A CT-scanneraccording to claim 1 or claim 4 and comprising at least one dataacquisition system (DAS) mounted on the rotor connected to the X-raydetectors that receives the signals generated by the X-ray detectors andgenerates digital data therefrom, portions of which digital data the atleast one DAS routes to each of The at least one transmitter.
 22. ACT-scanner according to claim 21 wherein the at least one DAS comprisesa plurality of DASs each of which acquires signals from differentdetectors.
 23. A method of transmitting to a desired location datacomprised in signals generated by X-ray detectors mounted on a rotor ofa gantry comprised in a CT-scanner, the method comprising: generatingfree space electromagnetic waves encoded with the data; sensing theelectromagnetic waves at the desired location; and decoding the sensedelectromagnetic wave to recover the data.
 24. A method according toclaim 23 wherein the data is encoded in accordance with a spreadspectrum code.
 25. A method according to claim 24 wherein the data isencoded in accordance with a time hopping impulse modulation (THIM)code.
 26. A method of transmitting to a desired location data comprisedin signals generated by X-ray detectors mounted on a rotor of a gantrycomprised in a CT-scanner, the method comprising: generating signalsencoded with the data in accordance with a spread spectrum code; sensingthe signals at the desired location; and decoding the sensed signals torecover the data.
 27. A method according to claim 26 wherein the code isa THIM code.
 28. A method according to claim 26 or claim 27 wherein thesignals encoded with the data are free space electromagnetic wavesencoded with the data.